[tp4tissue]

My guess @ what's actually happening to lordX2 is that the projector goes into a pc mode of sorts when fed 444 rgb full, on many systems this disables the dynamic brightness/contrast image manipulation of the projector itself. and it may well clamp to rec709 instead of native p3 gamut. This could account for the loss in perceived saturation both from the contrast and gamut difference. Potentially also following a different gamma curve

For an image to be rendered too brightly due to levels mismatch, The PC has to send the wrong 16-235 levels while the Projector is expecting 0-255. If that is NOT the case, then the projector is doing full rgb correctly.

This is why you need to check the 0,0,0 black, if that black is about the same, while comparing both modes with all dynamic contrast/iris settings disabled, THAT MEANS the projector is doing the RGB Full correctly.